1. FIELD OF THE INVENTION
The present invention relates to method and apparatus for continuously heating and melting a material to continuously obtain a melt at a desired temperature.
2. DESCRIPTION OF THE PRIOR ART
Cupola furnaces and crucible-type induction furnaces are well known and widely used melting cast iron. Cupolar furnaces are continuous melting furnaces by which refined melts of high quality can be continuously obtained, while induction furnaces are intermittent melting furnaces which allow fine materials to be used and components to be easily adjusted. Since both types of the furnaces have advantages and disadvantages, a double melting method which employs the combination of the two types of furnaces is now widely used. This sort of technique is disclosed in, for example, Japanese Patent Examined Publication No. 52-48564.
It is necessary to blow a large quantity of air in a cupola furnace for the purpose of burning coke at high temperature. Since the gas flow rate in the furnace is high, therefore, it is difficult to melt fine materials such as pig iron turning because they are oxidized or discharged to the outside of the furnace by the gas flow before they are melted. When it is required to obtain a melt at a high temperature, particularly, a temperature higher than 1,500.degree. C., incomplete combustion of coke tends to occur so as to decrease the efficiency and lower the controllability of temperature.
On the other hand, a refining effect cannot be expected from an induction furnace because material is melted simply by induction, heating. The induction furnace also has a problem in that it is inconvenient to supply a melt to a continuous casting apparatus because the furnace is intermittently operable intermittently.
In addition, although an attempt has been made to heat material by using an induction coil provided at an upper part of a cupola furnace in the prior art (Japanese Patent Examined Publication No. 52-48564 referred to above), no consideration has been made of the heating of a coke layer. Thus, the disadvantage caused by the blowing of a large quantity of air has not been eliminated, and the method of efficiently obtaining high temperatures has not been improved.
Namely, the above-mentioned double melting method employing the combination of an induction furnace and a combustion furnace is a proposal concerning a continuous refining technique in which electromagnetic induction heating and combustion heating using a burner are used for heating a low-temperature portion and a high-temperature portion, respectively. However, this proposal has the problems discussed below and does not reach a practical level.
Namely, although induction heating is used for heating a low-temperature portion in which a material to be melted is charged, the induction heating preheats only the metal to be melted. The preheating uses electric power and thus is costly and not practical. In addition, since a combustion method using a burner is used for heating the high-temperature portion, this method suffers from a decrease in the efficiency caused by the production of CO due to incomplete combustion of fuel, an increase in the size of the apparatus used and the necessity for a pollution prevention measure, which are caused by the occurrence of a large amount of exhaust gases, and the difficulty in melting a fine material to be melted because it tends to be dispersed by a gas flow. There also, problems that reduction proceeds insufficiently due to the oxidation of metal by the oxygen in the gas used, and satisfactory refinement cannot be easily obtained due to the production of a slug of the oxidized material.